1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a facsimile apparatus, a copier or a combined apparatus based on an electrophotographic system whereby an image is developed using minute particles such as toner, and in particular relates to a process cartridge that is used in an image forming apparatus and to a developing device used in the process cartridge.
2. Description of the Related Art
The developer carrier that is employed in an electrophotographic apparatus is located in position with a minute gap or making very slight contact with respect to the image carrier. The location means may be means that completely fixes the developer carrier and the image carrier or may be means that presses the developer carrier in the image carrier direction. In such a configuration, typically the drive force onto the developer carrier is transmitted by gears.
If the developer carrier, which is the rotating body, is of a configuration that is driven at one end side in the direction of its axis of rotation, a difference between left and right (difference between the drive side and the side opposite to the drive side) may be generated in the pressing force applied to the image carrier by the gear drive force that is received on one side.
A technique relating to a developing device that supplies developer to the image carrier and comprising a developer carrier that is driven in rotation by drive force applied to a gear provided on the shaft thereof, so that the developer carrier is pressed in the direction of the image carrier is proposed in Japanese Patent Application Laid-open No. H10-282752 (called Prior Art 1) and Japanese Patent Application Laid-open No. H09-106184 (called Prior Art 2).
Prior Art 1 proposes a technique wherein a configuration is adopted such that the toner carrier is pressed in the direction of the center of rotation of the electrophotographic photosensitive body when drive force is transmitted to the toner carrier, and Prior Art 2 proposes a technique wherein positional location of the photosensitive body and the developing roller is effected by mutually pressing into contact the bearings of the photosensitive body and the bearings of the developing roller of the developing device by pressing the developing device towards the photosensitive body by a pressing spring. Thus, in the spring pressing type, even if the pressing force on the drive side is altered by applying a correction in an amount corresponding to the drive force, the end result is still that a difference is generated between the drive side and the side opposite to the drive side by variability of the torque.
Also, the method has been proposed of providing a gap roller or contacting roller at both ends of the developer carrier. However, in addition to increased costs, bending about the roller is produced in the developer carrier by the drive force, leading to the variability of the gap or contact nip in the axial direction with respect to the photosensitive body.
Thus, whichever of these is adopted, the problem that a left/right difference (difference between the drive side and the side opposite to the drive side) in the pressing force onto the image carrier is generated by the drive force of the gear being received on one side cannot be said to be solved.
Also, an image forming apparatus has been proposed in for example Japanese Patent Application Laid-open No. 2006-48018 (called Prior Art 3) having a configuration wherein the amount of the nip between the photosensitive body and the developing roller is set to a prescribed value by adjusting the distance between the shafts of the photosensitive body and the developing roller by means of an adjustment jig that rotates an eccentric bearing member that supports the developing roller. In such an image forming apparatus, an eccentric cam and a mechanically assembled component that rotates this must be assembled.
Technologies relating to the present invention are also disclosed in e.g. Japanese Patent Application Laid-open No. H02-868537.